Mobile communication networks are in widespread use throughout metropolitan regions of the world, and have come to be common in many places. Over the years a variety of mobile communication services have been developed, including different radio air interfaces. Conventional mobile communication devices are designed for use with a particular air interface, but presently manufacturers are designing mobile communication devices that can access multiple communication networks having different air interfaces. Initial multi-mode mobile communication devices simply used dedicated hardware for different communication networks, and the device essentially had to be reset to switch over to a different air interface. Since then advances in integration have allowed manufacturers to design “all in one” mobile communication devices which can communicate over a variety of air interfaces, re-using circuitry for each of the air interfaces. Some of these devices were even “dual camp” designs which allowed the device to operate on two different communication networks at the same time.
On the other side of the air interface, the infrastructure and fixed equipment operated by communication service providers or operators, communication networks have been expanding and integrating as well. For one, most communication networks, in addition to conventional circuit mobile telephony, offer data services, including messaging and Internet access. Furthermore, communication network operators have been forming partnerships to support each others' subscribers, making it easy for users to roam from one system to another.
Presently, mobile circuit-switched voice communication is considered a mature technology. Much of the industry now is focusing on enhancing data communication, applications, and services. Efforts range from simply increasing data throughput to live voice and video streaming using Internet Protocol (IP) based communication. As a result there are a variety of competing mobile data service technologies available in the marketplace. Many of these technologies are standardized and specified by various standards organizations, such as, for example, the International Telecommunications Union (ITU). Standards are defined and published for present systems, but at the same time standards for future services as well as changes to existing services are also being undertaken in these organizations.
Two examples of data communication networks and protocols that are of interest in the industry, presently, are the Evolved Universal Terrestrial Radio Access Network (E-UTRAN), specified by the 3GPP group as 3GPP TS 36.300, and the Evolved Data Optimized (EV-DO) network specified as the cdma2000 High Rate Packet Data Air Interface Specification. Both of these specifications are well known in the art, and specify incompatible air interfaces. However, these systems can be connected on the network side of the air interface, potentially allowing inter-system call handover. However, even with data calls, considering there may be high quality of service (QoS) applications using the data call, minimizing handover delay is necessary to avoid packet loss. One way a data call could be handed over from one system to another would be for the mobile communication device to have two transceivers, one for each air interface. While a call or data session is being serviced on one, the other transceiver could be used to make arrangements with a base station of the other system to prepare for a handover. The dual transceiver approach, however, adds substantial cost the mobile communication device, as well as size and weight. Therefore there is a need for a method by which a call can be handed over from one communication network to a different communication network without incurring substantial delay.